Pharmacology Autonomic Nervous System Pharmacology 2 — Questions and Answers
Question 1: A patient with pheochromocytoma requires surgical removal. Which alpha-blocker is used preoperatively to prevent hypertensive crisis?
- Prazosin
- Phenoxybenzamine (Correct answer)
- Tamsulosin
- Doxazosin
Correct answer: Phenoxybenzamine
Phenoxybenzamine is a non-selective, irreversible alpha-blocker used preoperatively in pheochromocytoma to prevent catecholamine-induced hypertensive crises.
Question 2: Which muscarinic receptor subtype is primarily responsible for the decrease in heart rate caused by vagal stimulation?
- M1
- M2 (Correct answer)
- M3
- M4
Correct answer: M2
M2 receptors in the sinoatrial node mediate the negative chronotropic effect of acetylcholine released by vagal stimulation.
Question 3: Bethanechol is used to treat postoperative urinary retention. What is its mechanism of action?
- Blocks muscarinic receptors
- Activates nicotinic receptors
- Directly stimulates muscarinic receptors (Correct answer)
- Inhibits acetylcholinesterase
Correct answer: Directly stimulates muscarinic receptors
Bethanechol is a direct-acting muscarinic agonist that stimulates bladder detrusor contraction without significant nicotinic activity.
Question 4: A patient takes a non-selective beta-blocker and later uses an epinephrine auto-injector. Which cardiovascular effect is most likely?
- Hypotension with reflex tachycardia
- Severe hypertension with bradycardia (Correct answer)
- Hypotension with bradycardia
- Tachycardia with vasodilation
Correct answer: Severe hypertension with bradycardia
With beta-blockade, epinephrine's alpha-1 vasopressor effect is unopposed, causing severe hypertension; the reflex bradycardia is enhanced by beta-blockade.
Question 5: Which drug causes mydriasis and cycloplegia by blocking muscarinic receptors in the eye?
- Pilocarpine
- Physostigmine
- Atropine (Correct answer)
- Neostigmine
Correct answer: Atropine
Atropine blocks M3 receptors on the iris sphincter and ciliary muscle, causing pupil dilation (mydriasis) and loss of accommodation (cycloplegia).
Question 6: Guanethidine lowers blood pressure by which mechanism?
- Blocking alpha-1 receptors
- Depleting norepinephrine from sympathetic nerve terminals (Correct answer)
- Stimulating central alpha-2 receptors
- Inhibiting MAO
Correct answer: Depleting norepinephrine from sympathetic nerve terminals
Guanethidine is taken up into adrenergic neurons and depletes norepinephrine stores, preventing sympathetic vasoconstriction.
Question 7: Which beta-2 agonist is used as a tocolytic to suppress premature uterine contractions?
- Metoprolol
- Ritodrine (Correct answer)
- Dobutamine
- Carvedilol
Correct answer: Ritodrine
Ritodrine is a selective beta-2 agonist that relaxes uterine smooth muscle and is used as a tocolytic agent.
Pharmacology Autonomic Nervous System Pharmacology 2
A patient with pheochromocytoma requires surgical removal.
Which alpha-blocker is used preoperatively to prevent hypertensive crisis?